*This tutorial is out of date in some aspects, though may still be helpful. In particular:**The latest version of the MELTS_Excel file (April 24th, 2018) works in Excel 2016, and can be downloaded from the OFM MELTS for Excel page; just copy and paste the MORB composition and P-T conditions in to run the tutorial example.**MELTS for Excel now implements the mixed H*_{2}O-CO_{2} fluid model (i.e. rhyolite-MELTS 1.0.2, 1.1.0 and 1.2.0 are available), as well as the pMELTS model. Isenthalpic, isentropic and isochoric constraints can be used, though all calculations are closed system (except for oxygen, if an fO_{2} buffer is imposed).*If you have any trouble running MELTS for Excel check out the Troubleshooting MELTS_Excel e.g. 'Server returned no results, giving up!' FAQ post!*

This topic will show you how to work through one page of the (old) MELTS tutorial, using the new Excel-MELTS interface to rhyolite-MELTS:

Testing MELTS installation using the sample input file - Try this firstThe page is part of the 'Getting Started: Testing and Examples' section of the MELTS manual, written by Mark Ghiorso for the original graphical-user-interface (GUI) version. The idea of this topic is to show the similarities and differences between his GUI and the new Excel-MELTS interface. Here we use one of the Excel-MELTS workbooks that will be used at the

MELTS Workshop, being held immediately prior to the Goldschmidt 2013 conference. The post will be updated once Excel-MELTS is finalized for general release.

The screen output in this particular example is from a run using Excel 2010 on Windows 7, but Excel-MELTS should work on all Windows machines running XP or later and either Excel 2010 or Excel 2013. Make sure you have a suitable version of Excel and then download the workbook from

this link on the MELTS Workshop website. The Excel_MELTS-Interface-morb.xlsm workbook comes with a pre-loaded composition that is very similar to that used in the original tutorial.

Double-click the workbook to open it using Excel. If you get a message about the file being corrupted, try right-clicking on the file, choose 'Properties' and then press the 'Unblock' button under Security at the bottom of the pop-up. You may need to enable editting and you should also enable macros. Excel-MELTS uses the rhyolite-MELTS model but this will give identical results to the original MELTS model for the bulk composition used here. The workbook should open on the 'Input' worksheet.

Note that the bulk composition in Excel-MELTS workshop is the same as in the

morb.melts file linked on the

Mac OS X rhyolite-MELTS download site but the

Morb.melts input file used in the original tutorial differs slightly in Cr2O3 content. So, the first thing we need to do is adjust the Cr2O3 content on the 'Input' worksheet to 0.03. The pressure used in the tutorial calculation was 500 bars; choose 'bar' from the drop down Unit menu and type 500 in the P input box. Finally the tutorial did not use an fO2 buffer so uncheck the 'fO2 constrained' box. When you are done the worksheet should look something like this:

Also, some phases were suppressed in the original tutorial because the solid solution models were still being developed / tested. None of the phases are stable for the run conditions of the tutorial example, so suppressing these phases has no effect. You can check out the 'Phases' worksheet to see where you would suppress phases, by unchecking the boxes, if you needed to.

Now let's look at the other worksheets. On the 'PT_sequence' worksheet you can enter the initial temperature (T1) as 1200

^{o}C, the final temperature (T2) as 1200

^{o}C, the temperature increment (Delta T) as 3

^{o}C. Change the units for pressure, as before, and set P1 and P2 to 500 bars. fO2 is unconstrained by default so there's no need to change this. The 'Results' worksheet gives composition and thermodynamic data for system, liquid, total solids (including water), and individual mineral phases for the most recently calculated equilibrium state. You can ignore the 'aux' worksheet, which is for bookkeeping.

The front-end looks very different to the one in the original tutorial, but the settings for the underlying MELTS algorithm are now almost the same as described in the 'Four things have been accomplished:' list there. Excel-MELTS doesn't have a fractional crystallization mode yet (it's under development) so we can't quite complete the third one.

Press the 'Find Liquidus' button. As long as your computer is connected to the internet the MELTS server will be contacted and will perform the calculation. You may notice a short pause. Affinity information is displayed once the calculation is complete, similar to the MELTS GUI. In this case, the liquidus phase is feldspar and it appears at the top of the list with near-zero affinity. The liquidus temperature (1220.3

^{o}C) is identical.

Unlike in the MELTS GUI or alphaMELTS, the liquidus temperature just found does not automatically become the new starting temperature. So you will need copy and paste the temperature from the 'Input' worksheet to the 'PT_sequence' worksheet. Press 'Run PT Sequence' and see it go! When the calculation is finished a second workbook opens up with lots of cool plots and tables of results. There isn't a direct equivalent of the

original output file but the information can all be found pretty easily. The 'liquid' worksheet and the

GUI liquid table have a similar format. Of course, at the moment only the first set of results match exactly (or least to within ~0.1%) but this will change soon.

With thanks to Guil Gualda!

Paula